1. Field of the Invention
This invention relates generally to the field of threaded connectors and in particular to threaded connectors for tubular goods having pin and box members.
2. Description of the Prior Art
The need for a threaded connector for tubular goods having an axial tensile capability substantially equal to that of the tubular goods has long been recognized. Additionally, increased burst pressure rating for the tubular goods has long been considered beneficial. By tubular goods it is to be understood that drill pipe, work tubing, production tubing, well casing and other such conduits used in a well are included. It is also to be understood that the use of the threaded connector of the present invention is not to be considered limited to such tubular goods.
In the design of tubular connections, critical boundary conditions must be considered, one of these boundary conditions being the requirement for a minimum thickness at the distal end or end-of-pin flat of the pin member in order to maintain ruggedness under manufacturing, transportation and field running and handling conditions. A geometry change at the end of the pin member that would increase the end-of-pin flat thickness would allow optimization of other critical performance features.
Current end-of-pin geometry restricts design optimization procedures and therefore restricts maximization of connection performance. Some commercially available tubular connections with current end-of-pin geometry are sold under the mark "Triple Seal" by the Hydril Company, the assignee of the present invention and application. Such "Triple Seal" connections have featured three positive metal-to-metal seals comprising a fourteen (14) degree external seal, a middle ninety (90) degree torque shoulder and seal and a fourteen (14) degree pin to box internal seal. The connections have been offered as two-step cylindrical threaded surfaces with modified buttress threads. A new generation of thread design sold under the marks, "Triple Seal II" or "MAC", also use the current end-of-pin geometry. The "Triple Seal II" or "MAC" designs also feature three positive metal-to-metal seals comprising fourteen (14) external seals, a middle shoulder and a fourteen (14) degree pin to box internal seal.
The end-of-pin geometry of the above mentioned designs requires that increased tensile strength and burst pressure rating be achieved by decreasing the pin radial thickness which therefore would allow an increase in the box radial thickness, but this would in turn present undesirable excessively thin end-of-pin flats. Also the current end-of-pin geometry does not offer optimal protection of internal and external sealing surfaces. Furthermore, the end-of-pin geometry of current designs is difficult to field repair without damaging the sealing surfaces.